1. Field of the Invention
The present invention relates to the field of hydrodynamic motors for disc drive data storage devices and, more particularly, to a spindle motor with one or more bearing surfaces having a wear resistant coating thereon.
2. Description of the Related Art
Disc drive data storage devices, known as xe2x80x9cWinchesterxe2x80x9d type disc drives, are well-known in the industry. In a Winchester disc drive, digital data is written to and read from a thin layer of magnetizable material on the surface of rotating discs. Write and read operations are performed through a transducer that is carried in a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes a self-acting air bearing surface. As the disc rotates, the disc drags air beneath the air bearing surface, which develops a lifting force that causes the slider to lift and fly several microinches above the disc surface.
In the current generation of disc drive products, the most commonly used type of actuator is a rotary moving coil actuator. The discs themselves are typically mounted in a xe2x80x9cstackxe2x80x9d on the hub structure of a brushless DC spindle motor. The rotational speed of the spindle motor is precisely controlled by motor drive circuitry, which controls both the timing and the power of commutation signals directed to the stator windings of the motor. Typical spindle motor speeds have been in the range of 3600 RPM. Although, current technology has increased spindle motor speeds to 7200 RPM, 10,000 RPM, 15,000 RPM and above.
One of the principal sources of noise in disc drive data storage devices is the spindle motor. Disc drive manufacturers have recently begun looking at replacing conventional ball or roller bearings in spindle motors with xe2x80x9chydroxe2x80x9d bearings, such as hydrodynamic or hydrostatic bearings. A hydrodynamic bearing relies on a fluid film which separates the bearing surfaces and is therefore much quieter and in general has lower vibrations than conventional ball bearings. A hydrodynamic bearing is a self-pumping bearing that generates a pressure internally to maintain the fluid film separation. A hydrostatic bearing requires an external pressurized fluid source to maintain the fluid separation. Relative motion between the bearing surfaces in a hydrodynamic bearing causes a shear element that occurs entirely within the fluid film such that no contact between the bearing surfaces occurs.
In a hydrodynamic bearing, a lubricating fluid or gas provides a bearing surface between, for example, a stationary member of the housing and a rotating member of the disc hub. Typical lubricants include oil or ferromagnetic fluids. Hydrodynamic bearings spread the bearing surface over a larger surface area in comparison with a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface decreases wobble or run-out between the rotating and fixed members.
Despite the presence of the lubricating fluid, in conventional hydrodynamic bearing spindle motors, the bearing surfaces are still subject to continuous wear. As a result, the gap between bearing surfaces gradually changes over the lifetime of the device, and often in a manner that is not uniform across the bearing surfaces. This results in reduced performance and eventual failure of the disk drive. Additionally, for a gas lubricated hydrodynamic bearing, low frictional properties for the bearing surfaces is also required.
Therefore, there exists a need in the art for a hydrodynamic fluid bearing surfaces having improved wear resistance as well as low frictional properties.
The disc drive data storage system of the present invention includes a housing having a central axis, a stationary member that is fixed with respect to the housing and coaxial with the central axis, and a rotatable member that is rotatable about the central axis with respect to the stationary member. A stator is fixed with respect to the housing. A rotor is supported by the rotatable member and is magnetically coupled to the stator. At least one data storage disc is attached to and is coaxial with the rotatable member. A hydrodynamic bearing couples the stationary member to the rotatable member. The hydrodynamic bearing includes at least one working surface with a wear resistant coating thereon.